蝌蚪中的战斗蝌蚪

据几位参加TD SAT备考计划的同学回忆,2019年10月16日School Day重复使用了2019年6月多套实验小众卷中的Napm313卷,其中一篇自然科学文章考到的话题是有一种青蛙卵在蛇发起第一次攻击后,能够感知到震动(并且能区分蛇带来的震动和暴雨带来的震动的不同),主动提前孵化,从而逃避蛇的攻击。这简直就是蝌蚪中的战斗蝌蚪,甚至有的蝌蚪还会吃自己的小伙伴!

今天我们就来给大家科普一下大自然里的一些战斗蝌蚪,阅读其实很有趣。储备好背景知识,考试不慌哦!

一、青蛙中的霸主

印度牛蛙“Indian Bullfrog”(也翻译成“亚洲虎纹蛙”)是一体型较大的青蛙,主要分布于印度、孟加拉、尼泊尔、缅甸、阿富汗、斯里兰卡等地。

印度牛蛙(亚洲虎纹蛙)

这种青蛙最大的特点是什么都吃,它的食谱包括各种昆虫、无脊椎动物、老鼠、鼩鼱、各种幼蛙、蚯蚓、小蛇、蜥蜴、小鸟等。在我们的印象里,一般都是青蛙被蛇吃,到了亚洲虎纹蛙这里,游戏规则就反过来了。印度牛蛙真是牛,可以说是青蛙中的“霸王蛙”。

不过,当青蛙太霸道也不行。很快,这种青蛙被更凶狠的家伙盯上了。从1990年代开始,泰国开始有人专门养殖这种青蛙,供人类食用。到了2000年代,有人把这种青蛙引进到印度安达曼群岛。

安达曼群岛位于印度次大陆以东1200公里,岛上原有两种小青蛙(安达曼树蛙和查克拉帕尼窄嘴蛙)。引进的亚洲虎纹蛙身长可达16厘米,至少比这两种小青蛙大三到五倍。于是这两种小青蛙就成了虎纹蛙的盘中餐。非但如此,“虎父无犬子”,虎纹蛙的蝌蚪也会吃这两种小青蛙的蝌蚪。有科学家做了实验,发现虎纹蛙的蝌蚪不但对其他青蛙的蝌蚪赶尽杀绝,还同类相食。没错,它们会吃自己的小伙伴

一只虎纹蛙蝌蚪一口把另一只虎纹蛙蝌蚪咬成两截

因为全世界只有安达曼群岛上才有安达曼树蛙和查克拉帕尼窄嘴蛙,所以这两种小青蛙的数量可能会因为引进了亚洲虎纹蛙而急剧减少。此外,这提醒我们,在世界上的其他地方,可能也有其它种类的引进青蛙的蝌蚪吃当地原有青蛙蝌蚪的情况。

二、科普原文简注

The Indian bullfrog, which is native to the Indian sub-continent, has recently invaded the Andaman archipelago. This group of islands lies about 1200 km east of the Indian mainland. The bullfrog was probably introduced to the archipelago in the early 2000s for human consumption.

consumption n. 吃;喝
the eating, drinking, or ingesting of something

In these tropical islands of the Bay of Bengal, this large frog – it can grow up to 160 mm in length, a good three to five times larger than the native frogs – has spread remarkably fast. This is cause for concern, both ecologically and economically. That’s because of the frog’s “anything goes” attitude to feeding. The adults prey on a host of endemic vertebrates, including fishes, frogs, lizards, snakes, and even birds. The bullfrog doesn’t even spare poultry, which many households on the islands keep, making their invasion a problem for the economy too.

a good three to five times中的good的意思是“adj.[用来强调数字]至少”
(used to emphasize that a number is at least as great as one claims)

endemic adj. (植物,动物)某地特有的
(of a plant or animal) native or restricted to a certain country or area

例句:They’re a good twenty years younger.
他们至少年轻20岁。

Our new study reveals that not only the adult bullfrogs pose a threat to the Andaman archipelago’s native frog species: their tadpoles do, too.

We conducted an experiment, simulating real-life conditions, which revealed that no individuals from two native frog species survived the feeding onslaught of the Indian bullfrog’s tadpoles. That’s a level of predation which has never been documented before for the tadpoles of any invasive frog.

onslaught n. 猛烈的攻击
(a fierce or destructive attack)

If native tadpoles are such easy prey for this carnivorous bullfrog’s tadpoles, their populations could face serious decline. They may even be entirely wiped out on the Andamans. New frog species are often discovered on these islands, and the bullfrog’s tadpoles could also put these at risk.

The Andaman tree frog and the Chakrapani’s narrow-mouthed frog are found only on the Andaman archipelago. There are many other plant and animals species that are endemic to the Andamans; this uniqueness in diversity has conferred the “biodiversity hotspot” tag on the archipelago.

The Indian bullfrog is a recent entrant to these isolated islands. It breeds in the same paddy field pools and plantations as the narrow-mouthed frog and the tree frog. As all three species breed at the onset of the south-west monsoon in May, their tadpoles begin the process of development together.

monsoon n.季风

We wanted to understand how native tadpoles responded to carnivorous bullfrog tadpoles. Would the native tadpoles be able to outmaneuver these tadpole predators? Would bullfrogs out-compete native tadpoles for food and slow down their growth and reduce survival?

outmaneuver vt. 以更好的机动性躲开
(evade an opponent by moving faster or with greater agility)

To answer these questions, we replicated the tadpoles’ breeding grounds by setting up paddling pools – the sort that are appropriate for humans aged between three and ten. Combining the three frogs in all possible permutations, we tasked ourselves with monitoring a total of 25 pools. We were interested in how the tadpoles fared in terms of survival and growth. Tadpole density and the food that’s available are known to affect these parameters, so we kept these equal for all treatments.

permutation n. 各种排列组合
(a way, especially one of several possible variations, in which a set or number of things can be ordered or arranged)

Each pool had a total of 30 tadpoles, with equal representation of species in the treatments with more than one species. We replenished each pool with 40g of submerged leaf litter and changed the water (containing zooplanktons) every week.
The stage was set.
As soon as the experiment commenced, the carnivorous bullfrog tadpoles started their feeding frenzy. They preyed on the two native species and even cannibalised each other.

frenzy adj. 狂热的状态或行为(或举动)
a state or period of uncontrolled excitement or wild behavior

cannibalize vt. 同类动物相食
(of an animal) eat (an animal of its own kind)

This happened so quickly that only three of the pools were left with any surviving native tadpoles in the first week. The native tadpoles had been completely exterminated from the mixed species pools by the third week.
Bullfrog tadpoles grew with each hunt, enabling them to prey upon even more hapless native tadpoles. When left to themselves, the native tadpoles did much better, with three in every four making it to the finish line of metamorphosis – that is, they eventually turned into frogs.

The bullfrog tadpoles were so voracious that we weren’t even able to answer one of our questions: Would bullfrogs slow down native tadpoles’ growth? That’s because we had no native tadpoles left to measure.
The Chakrapani’s narrow-mouthed frog and the Andaman tree frog tadpoles that were kept away from the chomping bullfrog tadpoles transformed into terrestrial juveniles (known as metamorphs) in 21 days and 38 days, respectively.

chomp vi. 使劲(大声地)咀嚼
munch or chew vigorously and noisily

Our experiment reveals that in natural conditions, native frogs – many of which breed in similar habitats as invasive bullfrogs – are highly vulnerable as tadpoles.
The findings also emphasise the potential impact that invasive bullfrog tadpoles can have at the level of populations. They can severely reduce the number of freshly minted metamorphs joining the native species populations. Of course, the situation is made more complicated in natural settings by the presence of other predators like dragonflies; and the availability of alternative food sources like mosquito larvae.

Still, our results suggest that the tadpole stage of Indian bullfrogs is to be taken seriously while understanding the impact of the species on native frogs. This may have implications elsewhere: the world is witnessing an accelerating rate of frog invasions. Invasive frog populations’ tadpoles could have a serious, damaging impact far beyond the Andamans.

作者介绍:

TD福利

最后,TD SAT教研组从SAT常考的杂志中找到了相关话题的原文,我们做了详细注解和翻译。请大家私戳小马甲发送暗号「提前孵化」即可领取资料哦~

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